Caves on Mars -- perhaps the nicest of niches for microbial life -- are likely to be found near volcanic areas. Shown here is a recent image taken by the Mars Global Surveyor of Olympus Mons, perhaps the largest volcano in the Solar System. Lava flows and leveed lava channels can be seen on the southeastern flank of Olympus Mons - flows covered by a thick mantle of dust. CREDIT: NASA/JPL/Malin Space Science System
